Side-edge type surface light emitting apparatus having multiple gradually-sloped peak-shaped prisms

ABSTRACT

In a side-edge type surface light emitting apparatus including a light guide plate having a light emitting surface and a light distribution controlling surface opposing each other, and a light incident surface and a counter light incident surface opposing each other on sides of the light emitting surface and the light distribution controlling surface; a light source disposed on the light incident surface; and a prism sheet having multiple peak-shaped prisms protruded toward the light emitting surface and in parallel with the light incident surface, each of the peak-shaped prisms has a definite apical shape and a definite apical height, and the peak-shaped prisms have a definite pitch. The peak-shaped prisms have sloped angles gradually changed from the light incident surface to the counter light incident surface.

This application claims the priority benefit under 35 U.S.C. § 119 toJapanese Patent Application No. JP2020-073402 filed on Apr. 16, 2020,which disclosure is hereby incorporated in its entirety by reference.

BACKGROUND Field

The presently disclosed subject matter relates to a side-edge typesurface light emitting apparatus, and more particularly, to theimprovement of a prism sheet.

Description of the Related Art

A side-edge type surface light emitting apparatus, which is constructedby a light guide plate with multiple light emitting elements such aslight emitting diode (LED) elements disposed on the side thereof, hasbroadly been used as a backlight for a display unit such as a liquidcrystal display (LCD) unit in terms of its thin and light structure.When the display unit is used in a public place, a narrow lightdistribution characteristic or a narrow-viewing characteristic isrequired to prevent others from viewing the display unit from the side.This is called the privacy effect.

FIG. 14 is a perspective view illustrating a prior art side-edge typesurface light emitting apparatus (see: JP2015-15083A (JP6184205B1) &US2015/0009711A1 (U.S. Pat. No. 9,366,798B2)).

In FIG. 14, a side-edge type surface light emitting apparatus isconstructed by a double-face prism light guide plate 1 having a lightemitting surface S_(e), a light distribution controlling surface S_(d)opposing the light emitting surface S_(e), alight incident surfaceS_(in1) and a counter light incident surface S_(in2) on the sides of thelight emitting surface S_(e) and the light distribution controllingsurface S_(d), multiple LED elements 2 disposed on the light incidentsurface S_(in1), a single-face prism sheet 3 disposed on the lightemitting surface S_(e), and a light reflecting sheet 4 disposed on theside of the light distribution controlling surface S_(d). Note that anLCD panel (not shown) is provided on the outer surface of the prismsheet 3. In this case, the light incident surface S_(in1) is located onthe down side, while the counter light incident surface S_(in2) islocated on the up side.

The single-face prism sheet 3 includes multiple triangular-shaped prisms3 a along the Y-direction, each of the prisms 3 a having the sametriangular-shaped configuration protruded downward viewed from the side.

In the side-edge type surface light emitting apparatus of FIG. 14, whenlight is introduced from the LED elements 2 into the light incidentsurface S_(in1) of the light guide plate 1, a part of the light isemitted from the light emitting surface S_(e) through the single-faceprism sheet 3 to the outside. As a result, the luminous intensity I₀ ata viewpoint S corresponding to the viewer's eyes apart from thesingle-face prism sheet 3 can be determined by I₁(−7°), I₂(0°), andI₃(+7°) and so on, wherein:

-   -   I₁(−7°) is a luminous intensity of light propagated at the        azimuth angle θ=−7° to the viewpoint S from an upper-side light        emitting area A₁ of the prism sheet 3 on the side of the counter        light incident surface S_(in2) in which the upper-side light        emitting area A₁ has a luminous intensity distribution I₁(θ)        symmetrical with respect to θ=0° (see FIG. 17);    -   I₂(0°) is a luminous intensity of light propagated at the        azimuth angle θ=0° to the viewpoint S from a center-side light        emitting area A₂ of the prism sheet 3 immediately below the        viewpoint S in which the center-side light emitting area A₂ has        a luminous intensity distribution I₂(θ) symmetrical with respect        to θ=0° (see FIG. 17); and    -   I₃(+7°) is a luminous intensity of light propagated at the        azimuth angle θ=+7° to the viewpoint S from a lower-side light        emitting area A₃ of the prism sheet 3 on the side of the light        incident surface S_(in1) in which lower-side light emitting area        A₃ has a luminous intensity distribution I₃(θ) symmetrical with        respect to θ=0° (see FIG. 17). In this case, I₁(θ)≈I₂(θ)≈I₃(θ).

On the other hand, a remainder of the light may leak from the lightdistribution controlling surface S_(d) to the light reflecting sheet 4.In this case, the light reflecting sheet 4 returns the remainder of thelight to the light guide plate 1. Note that, the light reflecting sheet4 can be replaced by a light absorbing sheet.

The light waveguide plate 1 of FIG. 14 will be explained next withreference to FIGS. 15, 16A and 16B.

In FIG. 15, which is a perspective view of the light waveguide plate 1of FIG. 14, the light waveguide plate 1 is made of a transparentmaterial such as acryl resin or polycarbonate resin. The light guideplate 1 is of a double prism type which has multiple upper-side prisms11 along the X-direction (light propagation direction) perpendicular tothe light incident surface S_(in1) on the light emitting surface S_(e)and multiple lower-side prisms 12 along the Y-direction in parallel withthe light incident surface S_(in) on the light distribution controllingsurface S_(d). When light from the LED elements 2 (see: FIG. 14) isincident to the light incident surface S_(in1), the light propagatesthrough the interior of the light guide plate 1, so that the light isreflected by the prisms 12 toward the prisms 11 to emit the light fromthe light emitting surface S_(e).

The prisms 11 protrude along the positive side of the Z-direction, i.e.,they are convex, and are arranged in parallel with the X-direction(propagation direction). In more detail, each of the prisms 11 has across section of an isosceles triangular shape or a semi-circular shape.

In FIG. 16A, which is a bottom view of the lower-side prisms 12 of FIG.15, and in FIG. 16B, which is a partial cross-sectional view of FIG.16A, multiple flat mirror finished surfaces 13 are provided on the lightdistribution controlling surface S_(d) along the X-direction, in orderto spread light to the inner part of the light guide plate 1. Thefarther from the light incident surface S_(in1) the flat mirror finishedsurfaces 13 are located, the smaller the width of the flat mirrorfinished surfaces 13 along the Y-direction at that location. Thesequences of the prisms 12, each including a sloped surface 12-1 with alarge angle α1 and a sloped surface 12-2 with a small angle α2 (<α1),are provided between the flat mirror finished surfaces 13. The fartherfrom the light incident surface S_(in1) the prisms 12 are located, thelarger the width of sequences of the prisms 12 along the Y-direction atthat location.

In FIG. 17, which is a cross-sectional view for explaining the operationof the light guide plate 1 and the prism sheet 3 of FIG. 14, some lightis totally reflected between the light emitting surface S_(e) and thelight distribution controlling surface S_(d), and then is refracted atthe light emitting surface S_(e) or the sloped surface 12-2 of one ofthe prisms 12. In this case, since the width of the flat mirror finishedsurfaces 13 and the width of the prisms 12 along the Y-direction arechanged along the X-direction, the luminous intensity distribution I(θ)of light L2 within the light emitting surface S_(e) of the light guideplate 1 can be uniform as shown in FIG. 18A where ND indicates a narrowdistribution and BD indicates a broad distribution. Thus, the light L2emitted from the light emitting surface S_(e) is neither disturbed nordiffused, but is refracted at a definite angle with respect to thenormal line of the light emitting surface S_(e). Further, the light L2of the light emitting surface S_(e) is converted by thetriangular-shaped prisms 3 a of the single-face prism sheet 3 intocollimated light L4. The collimated light L4 whose focal length F isinfinite has a luminous intensity distribution as shown in FIG. 18Bwhere ND′ indicates a narrow distribution and BD′ indicates a broaddistribution. The narrow distribution ND′ rather than the broaddistribution BD′ could exhibit a narrow-viewing characteristic.

On the other hand, some of the light L1 is leaked from the lightdistribution controlling surface S_(d) of the light guide plate 1 to thelight reflecting sheet 4.

In FIG. 17, assume that the viewpoint S₂ (not shown) is located above acenter of the prism sheet 3 (see: FIG. 20A), and each of the luminousintensity distributions I₁(θ), I₂(θ) and I₃(θ) for the light emittingareas A₁, A₂ and A₃, respectively, of the prism sheet 3 are given by thebroad distribution BD′ of FIG. 18B. In this case, the luminous intensitydistributions I₁(θ), I₂(θ) and I₃(θ) are approximately the same as eachother: I₁(θ)≈I₂(θ)≈I₃(θ). The luminous intensity I₁(−7°) of lightpropagated from the upper-side light emitting area A₁ to the center-sidelocated viewpoint S₂ is 20% of the luminous intensity I₂(0°) of lightpropagated from the center-side light emitting area A₂ to thecenter-side located viewpoint S₂, and the luminous intensity I₃(+7°) oflight propagated from the lower-side light emitting area A₃ to thecenter-side located viewpoint S₂ is 60% of the luminous intensity I₂(0°)of light propagated from the lower-side light emitting area A₂ to thecenter-side located viewpoint S₂. This will be now explained below.

FIG. 19A is a view for explaining the upper-side located viewpoint S₁ ofthe side-edge type surface light emitting apparatus of FIG. 14, FIG. 19Bis a luminous intensity distribution on the outer surface of the prismsheet 3 viewed from the upper-side located viewpoint S₁ of FIG. 19A, andFIG. 19C is a graph of the luminous intensity distribution taken alongthe line C-C of FIG. 19B.

As illustrated in FIG. 19A, an upper-side located viewpoint S₁ islocated at a degree of +5° with respect to a normal at the center of theprism sheet 3. In this case, the luminous intensity distribution viewedfrom the upper-side located viewpoint S₁ is strongly subjected to theluminous intensity I₁(0°) of light propagated from the upper-side lightemitting area A₁ of the prism sheet 3 to the upper-side locatedviewpoint S₁. In this case, the upper-side light emitting area A₁ has aluminous intensity distribution I₁(θ) symmetrical with respect to θ=0°.On the other hand, the luminous intensity I₂(+5°) of light propagatedfrom the center-side light emitting area A₂ of the prism sheet 3 to theupper-side located viewpoint S₁ is smaller than I₁(0°), and the luminousintensity I₃(+10°) of light propagated from the lower-side lightemitting area A₃ of the prism sheet 3 to the upper-side locatedviewpoint S₁ is much smaller than I₁(0°). In this case, the center-sidelight emitting area A₂ and the lower-side light emitting area A₃ haveluminous intensity distributions I₂(θ) and I₃(θ), respectively, whichare approximately the same as I₁(θ). That is, I₁(θ)≈I₂(θ)≈I₃(θ). As aresult, as illustrated in FIG. 19B, a bright area (bright line) BA isformed on the outer surface of the prism sheet 3 on the side of thecounter light incident surface S_(in2), while a dark area (dark band) DAis formed on the lower-side of the prism sheet 3 on the side of thelight incident surface S_(in1). Therefore, as illustrated in FIG. 19C,the average luminous intensity I_(av) is about 13000 cd/m², and thedifference ΔI in luminous intensity taken along the line C-C of FIG. 19Bis very large. Note that in FIGS. 19B and 19C, Δx is the deviation fromthe center between the light incident surface S_(in1) and the counterlight incident surface S_(in2).

FIG. 20A is a view for explaining the center-side located viewpoint S₂of the side-edge type surface light emitting apparatus of FIG. 14, FIG.20B is a luminous intensity distribution on the outer surface of theprism sheet 3 viewed from the center-side located viewpoint S₂ of FIG.20A, and FIG. 20C is a graph of the luminous intensity distributiontaken along the line C-C of FIG. 20B.

As illustrated in FIG. 20A, a center-side located viewpoint S₂ islocated at a normal at the center of the prism sheet 3. In this case,the luminous intensity distribution viewed from the center-side locatedviewpoint S₂ is strongly subjected to the luminous intensity I₂(0°) oflight propagated from the center-side light emitting area A₂ of theprism sheet 3 to the center-side located viewpoint S₂. On the otherhand, the luminous intensity I₁(−7°) of light propagated from theupper-side light emitting area A₁ of the prism sheet 3 to thecenter-side located viewpoint S₂ is smaller than I₂(0°), and theluminous intensity I₃(+7°) of light propagated from the lower-side lightemitting area A₃ of the prism sheet 3 to the center-side locatedviewpoint S₂ is smaller than I₂(0°). As a result, as illustrated in FIG.20B, a bright area (bright line) BA is formed on the outer surface ofthe prism sheet 3 on the middle side thereof, while dark areas (darkband) DA are formed on the upper-side and the lower-side of the prismsheet 3. As a result, as illustrated in FIG. 20C, the average luminousintensity I_(av) is about 13000 cd/m², and the difference ΔI or ΔI′ inluminous intensity taken along the line C-C of FIG. 20B is very large.

FIG. 21A is a view for explaining the lower-side located viewpoint S₃ ofthe side-edge type surface light emitting apparatus of FIG. 14, FIG. 21Bis a luminous intensity distribution on the outer surface of the prismsheet 3 viewed from the lower-side located viewpoint S₃ of FIG. 21A, andFIG. 21C is a graph of the luminous intensity distribution taken alongthe line C-C of FIG. 21B.

As illustrated in FIG. 21A, a lower-side located viewpoint S₃ is locatedat a degree of −5° with respect to a normal at the center of the prismsheet 3. In this case, the luminous intensity distribution viewed fromthe lower-side located viewpoint S₃ is strongly subjected to theluminous intensity I₃(0°) of light propagated from the lower-side lightemitting area A₃ of the prism sheet 3 to the lower-side locatedviewpoint S₃. On the other hand, the luminous intensity I₁(−5°) of lightpropagated from the center-side light emitting area A₂ of the prismsheet 3 to the lower-side located viewpoint S₃ is smaller than I₃(0°),and the luminous intensity I₁(−10°) of light propagated from theupper-side light emitting area A₁ of the prism sheet 3 to the lower-sidelocated viewpoint S₃ is much smaller than I₃(0°). As a result, asillustrated in FIG. 21B, a bright area (bright line) BA is formed on thelower-side surface of the prism sheet 3 on the side of the lightincident surface S_(in1), while a dark area (dark band) DA is formed onthe upper-side of the prism sheet 3 on the side of the counter lightincident surface S_(in2). As a result, as illustrated in FIG. 21C, theaverage luminous intensity I_(av) is about 13000 cd/m², and thedifference ΔI in luminous intensity taken along the line C-C of FIG. 21Bis very large.

In the side-edge type surface light emitting apparatus of FIG. 14,although the average luminous intensities viewed from the viewpoints S₁,S₂ and S₃ are the same such as 13000 cd/m², the luminous intensitydistributions viewed from any of the viewpoints S₁, S₂ and S₃ along thevertical direction (C-C) have a large difference ΔI (ΔI′), i.e., anon-uniformity. Also, when the viewpoint (the viewer's eyes) is movedfrom the upper side to the lower side or vice versa with respect to theprism sheet 3, the bright area (bright line) BA would move from theupper side to the lower side or vice versa with respect to the prismsheet 3, so that the dark area (dark band) DA would be emphasizedagainst the viewer.

SUMMARY

The presently disclosed subject matter seeks to solve one or more of theabove-described problems.

According to the presently disclosed subject matter, in a side-edge typesurface light emitting apparatus including a light guide plate having alight emitting surface and a light distribution controlling surfaceopposing each other, and a light incident surface and a counter lightincident surface opposing each other on sides of the light emittingsurface and the light distribution controlling surface; a light sourcedisposed on the light incident surface; and a prism sheet havingmultiple peak-shaped prisms protruded toward the light emitting surfaceand in parallel with the light incident surface, each of the peak-shapedprisms has a definite apical shape and a definite apical height, and thepeak-shaped prisms have a definite pitch. The peak-shaped prisms havesloped angles gradually changed from the light incident surface to thecounter light incident surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of the presently disclosedsubject matter will be more apparent from the following description ofcertain embodiments, taken in conjunction with the accompanyingdrawings, as compared with the prior art, wherein:

FIG. 1 is a perspective view illustrating an embodiment of the side-edgetype surface light emitting apparatus according to the presentlydisclosed subject matter;

FIG. 2A is a view for explaining the upper-side located viewpoint of theside-edge type surface light emitting apparatus of FIG. 1;

FIG. 2B is a luminous intensity distribution on each of the lightemitting areas of the prism sheet viewed from the upper-side locatedviewpoint of FIG. 2A;

FIG. 2C is a graph of the luminous intensity distribution viewed fromthe upper-side located viewpoint taken along the vertical line C-C ofFIG. 2A;

FIG. 3A is a view for explaining the center-side located viewpoint ofthe side-edge type surface light emitting apparatus of FIG. 1;

FIG. 3B is a luminous intensity distribution on each of the lightemitting areas of the prism sheet viewed from the center-side locatedviewpoint of FIG. 3A;

FIG. 3C is a graph of the luminous intensity distribution viewed fromthe center-side located viewpoint taken along the vertical line C-C ofFIG. 3A;

FIG. 4A is a view for explaining the lower-side located viewpoint of theside-edge type surface light emitting apparatus of FIG. 1;

FIG. 4B is a luminous intensity distribution on each of the lightemitting areas of the prism sheet viewed from the lower-side locatedviewpoint of FIG. 4A;

FIG. 4C is a graph of the luminous intensity distribution viewed fromthe lower-side located viewpoint taken along the vertical line C-C ofFIG. 4A;

FIG. 5 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet is 600 mm and thefocal length of the prism sheet is changed and the emitting light of thelight guide plate has a narrow distribution of FIG. 18A whose full widthat half maximum is 30° to 15°;

FIG. 6A is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 2A viewed from the upper-side locatedviewpoint S₁ in FIG. 5;

FIG. 6B is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 3A viewed from the center-side locatedviewpoint in FIG. 5;

FIG. 6C is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 4A viewed from the upper-side locatedviewpoint in FIG. 5;

FIG. 7 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet is 600 mm and thefocal length of the prism sheet is changed and the emitting light of thelight guide plate has a broad distribution of FIG. 18A whose full widthat half maximum is larger than 30° to 15°;

FIG. 8A is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 2A viewed from the upper-side locatedviewpoint in FIG. 7;

FIG. 8B is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 3A viewed from the center-side locatedviewpoint in FIG. 7;

FIG. 8C is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 4A viewed from the upper-side locatedviewpoint in FIG. 7;

FIG. 9 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet is 500 mm and thefocal length of the prism sheet is changed and the emitting light L2 ofthe light guide plate 1 has a narrow distribution of FIG. 18A whose fullwidth at half maximum is 30° to 15°;

FIG. 10A is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 2A viewed from the upper-side locatedviewpoint S₁ in FIG. 9;

FIG. 10B is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 3A viewed from the center-side locatedviewpoint in FIG. 9;

FIG. 10C is a luminous intensity distribution of the vertical directionC-C of the prism sheet of FIG. 4A viewed from the upper-side locatedviewpoint in FIG. 9;

FIG. 11 is an enlarged cross-sectional view of the triangular prism ofFIG. 2;

FIG. 12A is a cross-sectional view for explaining a modification of thetriangular prism of FIG. 11;

FIG. 12B is a cross-sectional photographic view for explaining amodification of the triangular prism of FIG. 11 where luminous intensityof the prism sheet B′ viewed from the center-side located viewpoint isuniform along the X-direction but non-uniform along the Y-direction;

FIG. 12C is a cross-sectional view for explaining a modification of thetriangular prism of FIG. 11;

FIG. 12D is a cross-sectional photographic view for explaining amodification of the triangular prism of FIG. 11 where luminous intensityof the prism sheet 3′ viewed from the center-side located viewpoint isalso uniform along the Y-direction;

FIGS. 13A, 13B, 13C and 13D are views for explaining an example of amethod for manufacturing the prism sheets 3′ and 3″ of FIGS. 12A and12C;

FIG. 14 is a perspective view illustrating a prior side-edge typesurface light emitting apparatus;

FIG. 15 is a perspective view of the light guide plate of FIG. 14;

FIG. 16A is a bottom view of the light guide plate of FIG. 15;

FIG. 16B is a partial cross-sectional view of FIG. 16A;

FIG. 17 is a cross-sectional view for explaining the operation of thelight guide plate and the prism sheet of FIG. 14;

FIG. 18A is a diagram showing the luminous intensity distribution of thelight guide plate of FIG. 17;

FIG. 18B is a diagram showing the luminous intensity distribution of theprism sheet of FIG. 17;

FIG. 19A is a view for explaining the upper-side located viewpoint ofthe side-edge type surface light emitting apparatus of FIG. 14;

FIG. 19B is a luminous intensity distribution on the outer surface ofthe prism sheet viewed from the upper-side located viewpoint of FIG.19A;

FIG. 19C is a graph of the luminous intensity distribution taken alongthe line C-C of FIG. 19B;

FIG. 20A is a view for explaining the center-side located viewpoint ofthe side-edge type surface light emitting apparatus of FIG. 14;

FIG. 20B is a luminous intensity distribution on the outer surface ofthe prism sheet viewed from the upper-side located viewpoint of FIG.20A;

FIG. 20C is a graph of the luminous intensity distribution taken alongthe line C-C of FIG. 20B;

FIG. 21A is a view for explaining the lower-side located viewpoint ofthe side-edge type surface light emitting apparatus of FIG. 14;

FIG. 21B is a luminous intensity distribution on the outer surface ofthe prism sheet viewed from the lower-side located viewpoint of FIG.21A; and

FIG. 21C is a graph of the luminous intensity distribution taken alongthe line C-C of FIG. 21B.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In FIG. 1, which is a cross-sectional view illustrating an embodiment ofthe side-edge type surface light emitting apparatus according to thepresently disclosed subject matter, a single-face prism sheet 3′ isprovided instead of the single-face prism sheet 3 of FIG. 14.

In FIG. 1, the single-face prism sheet 3′ has multiple triangular-shapedprisms 3′a each having the same triangular shape formed by a lightincident surface 3′a-1 and a light reflecting surface 3′a-2, where theapical angle of an apex A is definite, for example, 60°, the pitch P isdefinite and the height H is definite. Here, the origin (x=0) of theX-coordinate is defined by the location of the light incident surfaceS_(in1) and Δx is the deviation from the center location of the prismsheet 3′ corresponding to the center between the light incident surfaceS_(in1) and the counter incident surface S_(in2). Conventionally, theviewpoint S₂ (not shown) is located above the center location of theprism sheet 3′.

In a θ₊ region where Δx≤0, the triangular-shaped prisms 3′a aregradually rotated by an angle of θ₊ (θ₊≥0) with respect to their apexesA in the clockwise direction viewed from the negative side of theY-direction, so that the light incident surfaces 3′a-1 rise and thelight reflecting surfaces 3′a-2 fall. In this case, the farther thetriangular-shaped prisms 3′a from the center location Δx=0, the largerthe angle θ₊. In other words, the nearer the triangular-shaped prisms3′a to the light incident surface the larger the angle θ₊. On the otherhand, in a θ⁻ region where Δx>0, the triangular-shaped prisms 3′a aregradually rotated by an angle of θ⁻ (θ⁻<0) with respect to their apexesA in the counter clockwise direction viewed from the negative side ofthe Y-direction, so that the light incident surfaces 3′a-1 fall and thelight reflecting surfaces 3′a-2 rise. In this case, the farther thetriangular-shaped prisms 3′a from the center location Δx=0, the largerthe angle θ In other words, the nearer the triangular-shaped prisms 3′ato the counter light incident surfaces S_(in2), the larger the angle θ⁻.

For example, assume that d is the distance between the viewpoint S₂ andthe prism sheet 3′. In this case,

if d=400 mm,

θ₊=−0.0565·Δx (Δx≤0)

θ⁻=−0.0565·Δx (Δx>0)

Also, if d=500 mm,

θ₊=−0.0446·Δx (Δx≤0)

θ⁻=−0.0446·Δx (Δx>0)

Further, if d=600 mm,

θ₊=−0.0381·Δx (Δx≤0)

θ⁻=−0.0381·Δx (Δx>0)

Still, if d=700 mm,

θ₊=−0.0305·Δx (Δx≤0)

θ⁻=−0.0305·Δx (Δx>0).

Furthermore, if d=800 mm,

θ₊=−0.0286·Δx (Δ≤0)

θ⁻=−0.0286·Δx (Δx>0)

Generally,

θ=θ₊(θ⁻)=a·Δx

where a=−0.0285˜−0.0446

The above equation can be represented by

θ=a·x+b

where x is the X-coordinate of the triangular-shaped prism 3′a;

b is the angle of the triangular-shaped prism 3′a at the incident lightsurface S_(in1).

Of course, when the location of the viewpoint is changed, the aboveequations would be changed.

FIG. 2A is a view for explaining the upper-side located viewpoint S₁ ofthe side-edge type surface light emitting apparatus of FIG. 1, FIG. 2Bis a luminous intensity distribution on each of the light emitting areasA₁, A₂ and A₃ of the prism sheet 3′ viewed from the upper-side locatedviewpoint S₁ of FIG. 2A, and FIG. 2C is a graph of the luminousintensity distribution viewed from the upper-side located viewpoint S₁taken along the vertical line C-C of FIG. 2A.

As illustrated in FIG. 2A, the upper-side located viewpoint S₁ islocated at an angle of +5° with respect to a normal at the center of theprism sheet 3′. In this case, the luminous intensity distribution viewedfrom the upper-side located viewpoint S₁ is equally subjected to theluminous intensity I₁(θ₊+5°) of light propagated from the upper-sidelight emitting area A₁ of the prism sheet 3′ to the upper-side locatedviewpoint S₁, the luminous intensity I₂(+5°) of light propagated fromthe center-side light emitting area A₂ of the prism sheet 3′ to theupper-side located viewpoint S₁ and the luminous intensity I₃(θ⁻+5°) oflight propagated from the lower-side light emitting area A₃ of the prismsheet 3′ to the upper-side located viewpoint S₁. In this case, asillustrated in FIG. 2B, the upper-side light emitting area A₁ has aluminous intensity distribution I₁(θ) which is similar to the luminousintensity distribution I₂(θ) of the center-side light emitting area A₂but is shifted by the azimuth angle θ₊. Also, the lower-side lightemitting area A₃ has a luminous intensity distribution I₃(θ) which issimilar to the luminous intensity distribution I₂(θ) of the center-sidelight emitting area A₂ but is shifted by the azimuth angle θ⁻. That is,

I ₁(θ+θ₊)≈I ₂(θ)≈I ₃(θ+θ⁻)

where I₁(θ) is symmetrical with respect to θ=θ₊;

I₂(θ) is symmetrical with respect to θ=0°; and

I₃(θ) is symmetrical with respect to θ=θ⁻.

In FIG. 2B, the luminous intensity I₁(θ₊+5°) is 65% of the luminousintensity I₁(θ₊), the luminous intensity I₂(+5°) is 65% of the luminousintensity I₂(0°), and the luminous intensity I₃(θ⁻+5°) is 65% of theluminous intensity I₃(θ⁻). In this case, since I₁(θ₊)≈I₂(0°)≈I₃(θ⁻),

I ₁(θ₊+5°)≈I ₂(+5°)≈I ₃(θ⁻+5°)

Thus, the luminous intensity distribution viewed from the upper-sidelocated viewpoint S₁ is equally subjected to I₁(θ₊+5°), I₂(+5°) andI₃(θ⁻+5°) which are equal to each other.

As illustrated in FIG. 2C, which is a graph of the luminous intensitydistribution viewed from the upper-side located viewpoint S₁ taken alongthe vertical line C-C of FIG. 2A, the average luminous intensity I_(av)is small, i.e., about 15000 cd/m², but the difference ΔI in luminousintensity is very small. Also, a large bright area (bright line) BA isformed while small dark areas (dark bands) DA are formed. In FIG. 2C,note that Δx is the deviation from the center of the vertical line C-Cof FIG. 2A.

FIG. 3A is a view for explaining the center-side located viewpoint S₂ ofthe side-edge type surface light emitting apparatus of FIG. 1, FIG. 3Bis a luminous intensity distribution on each of the light emitting areasA₁, A₂ and A₃ of the prism sheet 3′ viewed from the center-side locatedviewpoint S₂ of FIG. 3A, and FIG. 3C is a graph of the luminousintensity distribution viewed from the center-side located viewpoint S₂taken along the vertical line C-C of FIG. 3A.

As illustrated in FIG. 3A, the upper-side located viewpoint S₂ islocated on a normal at the center of the prism sheet 3′. In this case,the luminous intensity distribution viewed from the center-side locatedviewpoint S₂ is equally subjected to the luminous intensity I₁(θ₊) oflight propagated from the upper-side light emitting area A₁ of the prismsheet 3′ to the center-side located viewpoint S₂, the luminous intensityI₂(0°) of light propagated from the center-side light emitting area A₂of the prism sheet 3′ to the center-side located viewpoint S₂ and theluminous intensity I₃(θ⁻) of light propagated from the lower-side lightemitting area A₃ of the prism sheet 3′ to the center-side locatedviewpoint S₂. Even in this case, as illustrated in FIG. 3B,

I ₁(θ+θ₊)≈I ₂(θ)≈I ₃(θ+θ⁻)

where I₁(θ) is symmetrical with respect to θ=θ₊;

I₂(θ) is symmetrical with respect to θ=0°; and

I₃(θ) is symmetrical with respect to θ=θ⁻.

In FIG. 3B, the luminous intensity I₁(θ₊) is 100% of the luminousintensity I₁(θ₊), the luminous intensity I₂(0°) is 100% of the luminousintensity I₂(0°), and the luminous intensity I₃(θ⁻) is 100% of theluminous intensity I₃(θ⁻). In this case, I₁(θ₊)≈I₂(0°)≈I₃(θ⁻).

Thus, the luminous intensity distribution viewed from the center-sidelocated viewpoint S₂ is equally subjected to I₁(θ₊), I₂(0°) and I₃(θ⁻)which are equal to each other.

As illustrated in FIG. 3C, which is a graph of the luminous intensitydistribution viewed from the center-side located viewpoint S₂ takenalong the vertical line C-C of FIG. 3A, the average luminous intensityI_(av) is large, i.e., about 24000 cd/m², and the difference ΔI inluminous intensity is very small. Also, a large bright area (brightline) BA is formed while small dark areas (dark bands) DA are formed. InFIG. 3C, note that Δx is the deviation from the center of the verticalline C-C of FIG. 3A.

FIG. 4A is a view for explaining the lower-side located viewpoint S₃ ofthe side-edge type surface light emitting apparatus of FIG. 1, FIG. 4Bis a luminous intensity distribution on each of the light emitting areasA₁, A₂ and A₃ of the prism sheet 3′ viewed from the lower-side locatedviewpoint S₃ of FIG. 4A, and FIG. 4C is a graph of the luminousintensity distribution viewed from the lower-side located viewpoint S₃taken along the vertical line C-C of FIG. 4A.

As illustrated in FIG. 4A, the lower-side located viewpoint S₃ islocated at an angle of −5° with respect to a normal at the center of theprism sheet 3′. In this case, the luminous intensity distribution viewedfrom the lower-side located viewpoint S₃ is equally subjected to theluminous intensity I₁(θ₊−5°) of light propagated from the upper-sidelight emitting area A₁ of the prism sheet 3′ to the lower-side locatedviewpoint S₃, the luminous intensity I₂(−5°) of light propagated fromthe center-side light emitting area A₂ of the prism sheet 3′ to thelower-side located viewpoint S₃ and the luminous intensity I₃(θ⁻−5°) oflight propagated from the lower-side light emitting area A₃ of the prismsheet 3′ to the lower-side located viewpoint S₃. Even in this case, asillustrated in FIG. 4B,

I ₁(θ+θ₊)≈I ₂(θ)≈I ₃(θ+θ⁻)

where I₁(θ) is symmetrical with respect to θ=θ₊;

I₂(θ) is symmetrical with respect to θ=0°; and

I₃(θ) is symmetrical with respect to θ=θ⁻.

In FIG. 4B, the luminous intensity I₁(θ₊−5°) is 60% of the luminousintensity I₁(θ₊), the luminous intensity I₂(−5°) is 60% of the luminousintensity I₂(0°), and the luminous intensity I₃(θ⁻−5°) is 60% of theluminous intensity I₃(θ⁻). In this case, since I₁(θ₊)≈I₂(0°)≈I₃(θ⁻),

I ₁(θ₊−5°)≈I ₂(−5°)≈I ₃(θ⁻−5°)

Thus, the luminous intensity distribution viewed from the lower-sidelocated viewpoint S₃ is equally subjected to I₁(θ₊−5°), I₂(−5°) andI₃(θ⁻−5°) which are equal to each other.

As illustrated in FIG. 4C, which is a graph of the luminous intensitydistribution viewed from the lower-side located viewpoint S₃ taken alongthe vertical line C-C of FIG. 4A, the average luminous intensity I_(av)is small, i.e., about 14000 cd/m², but the difference ΔI in luminousintensity is very small. Also, a large bright area (bright line) BA isformed while small dark areas (dark bands) DA are formed. In FIG. 4C,note that Δx is the deviation from the center of the vertical line C-Cof FIG. 4A.

In the side-edge type surface light emitting apparatus of FIG. 1, theaverage luminous intensity I_(av) viewed from the center-side locatedviewpoint S₂ is large and the average luminous intensities I_(av) viewedfrom the upper-side located viewpoint S₁ and the lower-side locatedviewpoint S₃ are small; however, the luminous intensity distributionsviewed from any of the viewpoints S₁, S₂ and S₃ along the verticaldirection (C-C) have a small difference ΔI in luminous intensity, i.e.,uniformity. Also, when the viewpoint (the viewer's eyes) is moved fromthe upper side to the lower side or vice versa with the prism sheet 3′,the bright area (bright line) BA would not move from the upper side tothe lower side or vice versa due to the large size thereof, so that thedark area (dark band) DA would not be emphasized from the viewpoint ofthe viewer due to the small size thereof.

FIG. 5 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet 3′ is 600 mm andthe focal length F of the prism sheet 3′ is changed and the emittinglight L2 of the light guide plate 1 has a narrow distribution ND of FIG.18A whose full width at half maximum is 30° to 15°.

FIG. 6A is a luminous intensity distribution of the vertical directionC-C of the prism sheet 3′ of FIG. 2A viewed from the upper-side locatedviewpoint S₁ in FIG. 5, FIG. 6B is a luminous intensity distribution ofthe vertical direction C-C of the prism sheet 3′ of FIG. 3A viewed fromthe center-side located viewpoint S₂ in FIG. 5, and FIG. 6C is aluminous intensity distribution of the vertical direction C-C of theprism sheet 3′ of FIG. 4A viewed from the upper-side located viewpointS₃ in FIG. 5.

As illustrated in FIGS. 5, 6A, 6B and 6C, when the focal length Fcoincides with the distance d (=600 mm), the average luminous intensityI_(av) viewed from the center-side located viewpoint S₂ is large, i.e.,27000 cd/m² while the average luminous intensities I_(av) viewed fromthe upper-side located viewpoint S₁ and the lower-side located viewpointS₃ are low, i.e., 16000 cd/m², but the difference ΔI in luminousintensity viewed from any of the viewpoints S₁, S₂ and S₃ is very small,so that the luminous intensity can be uniform. Therefore, when theviewpoint is moved from an upper location to a lower location or viceversa, the bright area BA would hardly be moved, so that the dark areaDA would not be emphasized. On the other hand, when the focal length Fis 400˜500 mm or 700˜800 mm, the difference ΔI in luminous intensityviewed from any of the viewpoints S₁, S₂ and S₃ become large, so thatthe resolution of the focal length F by the gradual change of therotational angle θ₊ (θ⁻) of the triangular prisms 3′a can be increasedby the narrow distribution characteristic. Therefore, when the distanced between the viewpoint and the prism sheet 3′ is 600 mm, the focallength F is preferably 600 to 700 mm.

FIG. 7 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet 3′ is 600 mm andthe focal length F of the prism sheet 3′ is changed and the emittinglight L2 of the light guide plate 1 has a broad distribution BD of FIG.18A whose full width at half maximum is larger than 30° to 15°.

FIG. 8A is a luminous intensity distribution of the vertical directionC-C of the prism sheet 3′ of FIG. 2A viewed from the upper-side locatedviewpoint S₁ in FIG. 7, FIG. 8B is a luminous intensity distribution ofthe vertical direction C-C of the prism sheet 3′ of FIG. 3A viewed fromthe center-side located viewpoint S₂ in FIG. 7, and FIG. 8C is aluminous intensity distribution of the vertical direction C-C of theprism sheet 3′ of FIG. 4A viewed from the upper-side located viewpointS₃ in FIG. 7.

As illustrated in FIGS. 7, 8A, 8B and 8C, when the focal length Fcoincides with the distance d (=600 mm), the average luminous intensityI_(av) viewed from the center-side located viewpoint S₂ is large, i.e.,27000 cd/m² while the average luminous intensities I_(av) viewed fromthe upper-side located viewpoint S₁ and the lower-side located viewpointS₃ are low, i.e., 15000˜16000 cd/m², but the difference ΔI in luminousintensity viewed from any of the viewpoints S₁, S₂ and S₃ is very small,so that the luminous intensity can be uniform. Therefore, when theviewpoint is moved from an upper location to a lower location or viceversa, the bright area BA would hardly be moved, so that the dark areaDA would not be emphasized. On the other hand, when the focal length Fis 400˜500 mm or 700˜800 mm, the difference ΔI in luminous intensityviewed from any of the viewpoints S₁, S₂ and S₃ become large, so thatthe resolution of the focal length F by the gradual change of therotational angle θ₊ (θ⁻) of the triangular prisms 3′a can be decreasedby the broad distribution characteristic. Therefore, when the distance dbetween the viewpoint and the prism sheet 3′ is 600 mm, the focal lengthF is preferably 600 to 650 mm.

Thus, when the emitting light of the light guide plate 1 has a narrowdistribution characteristic ND as illustrated in FIG. 18A, theresolution of the focal length F by the gradual change of the rotationalangle θ₊ (θ⁻) of the triangular-shaped prisms 3′a can be increased bythe principle of superposition of the distributions.

FIG. 9 depicts photos of the luminous intensity distributions of theside-edge type surface light emitting apparatus of FIG. 1 where thedistance d between the viewpoint and the prism sheet 3′ is 500 mm andthe focal length F of the prism sheet 3′ is changed and the emittinglight L2 of the light guide plate 1 has a narrow distribution ND of FIG.18A whose full width at half maximum is 30° to 15°.

FIG. 10A is a luminous intensity distribution of the vertical directionC-C of the prism sheet 3′ of FIG. 2A viewed from the upper-side locatedviewpoint S₁ in FIG. 9, FIG. 10B is a luminous intensity distribution ofthe vertical direction C-C of the prism sheet 3′ of FIG. 3A viewed fromthe center-side located viewpoint S₂ in FIG. 9, and FIG. 10C is aluminous intensity distribution of the vertical direction C-C of theprism sheet 3′ of FIG. 4A viewed from the upper-side located viewpointS₃ in FIG. 9.

As illustrated in FIGS. 9, 10A, 10B and 10C, when the focal length Fcoincides with the distance d (=500 mm), the average luminous intensityI_(av) viewed from the center-side located viewpoint S₂ is large, i.e.,27000 cd/m² while the average luminous intensities I_(av) viewed fromthe upper-side located viewpoint S₁ and the lower-side located viewpointS₃ are low, i.e., 14000˜15000 cd/m², but the difference ΔI in luminousintensity viewed from any of the viewpoints S₁, S₂ and S₃ is very small,so that the luminous intensity can be uniform. Therefore, when theviewpoint is moved from an upper location to a lower location or viceversa, the bright area BA would hardly be moved, so that the dark areaDA would not be emphasized. On the other hand, when the focal length Fis 400 mm or 600 mm, the difference ΔI in luminous intensities viewedfrom the viewpoints S₁ and S₃ become opposite to each other, so that theresolution of the focal length F by the gradual change of the rotationalangle θ₊ (θ⁻) of the triangular prisms 3′a can be increased by thenarrow distribution characteristic. Therefore, when the distance dbetween the viewpoint and the prism sheet 3′ is 500 mm, the focal lengthF is preferably 500 mm.

FIG. 11 is a cross-sectional view of the triangular-shaped prisms 3′a ofFIG. 1.

As illustrated in FIG. 11, each of the triangular-shaped prisms 3′a hasan apex A whose apical angle is definite such as 60°, a definite pitch Pand a definite height H. In this case, the distance D of a flat portionbetween the triangular-shaped prisms 3′a defined by the light reflectingsurface 3′a-2 of one triangular-shaped prism and the light incidentsurface 3′a-1 of its adjacent triangular-shaped prism is changed inaccordance with the rotational angle θ (θ⁻) of the triangular prisms3′a. Therefore, the height H is so determined that the distance D islarger than a predetermined value, regardless of the rotational angle θ₊(θ⁻) of the triangular prisms 3′a. As a result, when manufacturing theprism sheet 3′ of FIG. 1 using molds, the molds can easily be extractedto enhance the manufacturing yield.

FIGS. 12A, 12B, 12C and 12D are views for explaining a modification ofthe triangular shaped prisms 3′a of FIG. 1.

In FIG. 1, the triangular-shaped prisms 3′a are provided in parallelwith the light incident surface S_(in1), i.e., along with theY-direction. As a result, as illustrated in FIG. 12B, the luminousintensity of the prism sheet B′ viewed from the center-side locatedviewpoint is uniform along the X-direction but non-uniform along theY-direction. On the other hand, as illustrated in FIG. 12C, a prismsheet 3″ is provided with triangular-shaped prisms 3″ a which areconcave toward the light incident surface S_(in1). As a result, asillustrated in FIG. 12D, the luminous intensity of the prism sheet 3′viewed from the center-side located viewpoint is also uniform along theY-direction.

FIGS. 13A, 13B, 13C and 13D are views for explaining an example of amethod for manufacturing the prism sheets 3′ and 3″ of FIGS. 12A and12C.

Firstly, as illustrated in FIG. 13A, a prism sheet 3′ L larger than aprism sheet 3′ is manufactured. Similarly, as illustrated in FIG. 13B, aprism sheet 3″ L larger than a prism sheet 3″ is manufactured. In FIG.13A or 13B, the rotational angle θ=0° (Δx=0) is located at the center ofthe prism sheet 3′ L or 3″ L.

Next, as illustrated in FIG. 13A or 13B, when the prism sheet 3′ L or 3″L is cut at a cut position C1, the prism sheet 3′ or 3″ as illustratedin FIG. 13C can be obtained. In this case, a center-side locatedviewpoint S₂ coincides with the center position (Δx=0) defined by thecenter PC of the prism sheet 3′ or 3″.

On the other hand, as illustrated in FIG. 13A or 13B, when the prismsheet 3′ L or 3″ L is cut at a cut position C2, the prism sheet 3′ or 3″as illustrated in FIG. 13D can be obtained. In this case, an upper-sidelocated viewpoint S₁ coincides with the center position (Δx=0) definedby a position upward the center PC of the prism sheet 3′ or 3″.

Thus, the position of the viewpoint and the center position (Δx=0) cansimply be changed by changing the cut position C1 or C2 of the largesized prism sheet 3′ L or 3″ L.

As explained above, the center position (Δx=0) does not always coincidewith the center position between the light incident surface S_(in1) andthe counter light incident surface S_(in2) the center position (Δx=0)can be near the light incident surface S_(in1) or near the counter lightincident surface S_(in2) as illustrated in FIG. 13C.

Also, the triangular-shaped prisms 3′ and 3″ a do not always have atriangular shape; the triangular shape can be replaced by a peak shapehaving a curved apex.

Further, since the side-edge type surface light emitting apparatus canhave a narrow distribution characteristic, the side-edge type surfacelight emitting apparatus according to the presently disclosed subjectmatter can be applied to an LCD unit exhibiting the privacy effect.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the presently disclosedsubject matter without departing from the spirit or scope of thepresently disclosed subject matter. Thus, it is intended that thepresently disclosed subject matter covers the modifications andvariations of the presently disclosed subject matter provided they comewithin the scope of the appended claims and their equivalents. Allrelated or prior art references described above and in the Backgroundsection of the present specification are hereby incorporated in theirentirety by reference.

1. A side-edge type surface light emitting apparatus comprising: a lightguide plate having a light emitting surface and a light distributioncontrolling surface opposing each other, and a light incident surfaceand a counter light incident surface opposing each other on sides ofsaid light emitting surface and said light distribution controllingsurface; a light source disposed on said light incident surface; and aprism sheet having multiple peak-shaped prisms protruded toward saidlight emitting surface and in parallel with said light incident surface,each of said peak-shaped prisms having a definite apical shape and adefinite apical height, said peak-shaped prisms having a definite pitch,said peak-shaped prisms having sloped angles gradually changed from saidlight incident surface to said counter light incident surface.
 2. Theside-edge type surface light emitting apparatus as set forth in claim 1,wherein the gradually-sloped angles of said peak-shaped prisons arechanged linearly in accordance with a distance between each of saidpeak-shaped prisms and said light incident surface.
 3. The side-edgetype surface light emitting apparatus as set forth in claim 1, whereineach of said peak-shaped prisms has a light incident prism surface and alight reflecting prism surface sandwiching an apex thereof, the nearerto said light incident surface and the farther from a center location ofsaid light guide plate, the light reflecting prism surfaces of saidpeak-shaped prisms gradually falling, the nearer to said light incidentsurface and the farther from the center location of said light guideplate, the light reflecting prism surfaces of said peak-shaped prismsgradually falling.
 4. The side-edge type surface light-emittingapparatus as set forth in claim 3, wherein the center location of saidprism sheet is equidistant from said light incident surface and saidcounter light incident surface.
 5. The side-edge type surfacelight-emitting apparatus as set forth in claim 3, wherein the centerlocation of said prism sheet is non-equidistant from said light incidentsurface and said counter light incident surface.
 6. The side-edge typesurface light emitting apparatus as set forth in claim 1, wherein thegradually sloped angles of said peak-shaped prisms are given byrotational angles of said peak-shaped prisms.
 7. The side-edge typesurface light emitting apparatus as set forth in claim 6, wherein therotational angles of said peak-shaped prisms are given byθ=a·x+b where x is a distance between each of said peak-shaped prismsand said light incident surface, a is from −0.0285 to −0.0446, and b isthe rotational angle of one of said peak-shaped prisms on said lightincident surface.
 8. The side-edge type surface light emitting apparatusas set forth in claim 1, wherein each of said peak-shaped prisms has alight incident prism surface and a light reflecting prism surfacesandwiching an apex thereof, said prism sheet having a flat portionbetween the light reflecting prism surface of one of said peak-shapedprisms and the light incident prism surface of its adjacent one of saidpeak-shaped prisms.
 9. The side-edge type surface light emittingapparatus as set forth in claim 1, wherein said peak-shaped prisms areconcave against said light incident surface.
 10. The side-edge typesurface light emitting apparatus as set forth in claim 1, wherein eachof said peak-shaped prisms comprises a triangular-shaped prism.
 11. Theside-edge type surface light emitting apparatus as set forth in claim 1,wherein said light guide plate comprises: multiple upper-side prismsprovide on said light emitting surface perpendicular to said lightincident surface; multiple flat mirrors provided on said lightdistribution controlling surface in parallel with said light incidentsurface; and multiple lower-side prisms provided on said lightdistribution controlling surface where said flat mirrors are notprovided, said tower-side prisms protruded from said flat mirrors.